1. Field of the Invention
The present invention relates to a method for irradiating an electromagnetic pulse on an object, analyzing the obtained electromagnetic pulse to obtain information regarding the object, and a tomography device employing the same.
2. Description of the Related Art
In recent years, there have been developed various inspection techniques employing electromagnetic waves of which the frequency is in a range of 30 GHz to 30 THz, so-called terahertz (THz) waves. Nondestructive inspections taking advantage of transmission properties of terahertz waves are an example. Japanese Laid-Open Patent Publication No. 2004-28618 discloses an example in which a terahertz-band electromagnetic wave pulse is irradiated on a coating film which is a sample, and a reflected electromagnetic wave pulse is detected and analyzed by time-domain spectroscopy (TDS). The film thickness of each coating film formed in multilayers is calculated by checking time difference between peaks of pulses included in the detected signals. Also, directing attention to waveforms of peaks enables the state of each coating film, for example, how dry the film is, to be recognized from changes thereof.
On the other hand, there is also an example of checking the material of a sample from a viewpoint of spectroscopy, employing absorption in a terahertz band of a sample. Japanese Laid-Open Patent Publication No. 10-153547 describes determining a sample by irradiating terahertz-band electromagnetic wave pluses on the sample, and checking the spectrum of transmitted or reflected electromagnetic wave pluses. TDS allows obtaining of location information of each coating film as with the former, or obtaining of the optical property of a sample as with the latter, in order to obtain the amplitude and phase of an electric field at the same time.
However, in the case of the method disclosed in Japanese Laid-Open Patent Publication No. 2004-28618, when the thickness of a layer of a multilayer sample is the same as with the width of an electromagnetic wave pulse within this layer, it is difficult to separate a peak waveform corresponding to each interface of two sides. Also, in the event that a peak waveform derived from multiple reflections within a layer happens to be overlapped with a peak waveform derived from another interface, separation is also difficult in the same way. As a result, there have been cases where identification of the thickness or material of a layer of interest is not performed suitably. On the other hand, with the method disclosed in Japanese Laid-Open Patent Publication No. 10-153547, in the event that a sample has a multilayered structure, it is difficult to individually identify the material of each layer.
Thus, measurement of multilayer samples according to the related art has a problem in that it is difficult to recognize the thickness and material of each layer at the same time.